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net: introduce skb_list_walk_safe for skb segment walking

commit dcfea72e79 upstream.

As part of the continual effort to remove direct usage of skb->next and
skb->prev, this patch adds a helper for iterating through the
singly-linked variant of skb lists, which are used for lists of GSO
packet. The name "skb_list_..." has been chosen to match the existing
function, "kfree_skb_list, which also operates on these singly-linked
lists, and the "..._walk_safe" part is the same idiom as elsewhere in
the kernel.

This patch removes the helper from wireguard and puts it into
linux/skbuff.h, while making it a bit more robust for general usage. In
particular, parenthesis are added around the macro argument usage, and it
now accounts for trying to iterate through an already-null skb pointer,
which will simply run the iteration zero times. This latter enhancement
means it can be used to replace both do { ... } while and while (...)
open-coded idioms.

This should take care of these three possible usages, which match all
current methods of iterations.

skb_list_walk_safe(segs, skb, next) { ... }
skb_list_walk_safe(skb, skb, next) { ... }
skb_list_walk_safe(segs, skb, segs) { ... }

Gcc appears to generate efficient code for each of these.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[ Just the skbuff.h changes for backporting - gregkh]
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
5.4-rM2-2.2.x-imx-squashed
Jason A. Donenfeld 2020-01-08 16:59:02 -05:00 committed by Greg Kroah-Hartman
parent 760e9fd4f7
commit aa350dbe3a
1 changed files with 5 additions and 0 deletions

View File

@ -1480,6 +1480,11 @@ static inline void skb_mark_not_on_list(struct sk_buff *skb)
skb->next = NULL;
}
/* Iterate through singly-linked GSO fragments of an skb. */
#define skb_list_walk_safe(first, skb, next) \
for ((skb) = (first), (next) = (skb) ? (skb)->next : NULL; (skb); \
(skb) = (next), (next) = (skb) ? (skb)->next : NULL)
static inline void skb_list_del_init(struct sk_buff *skb)
{
__list_del_entry(&skb->list);